The main components of a motor vehicle drive train are a drive assembly and a transmission. The transmission converts torques and rotational speeds, and thereby transmits the traction force provided by the drive assembly. The present invention concerns a method for operating a drive train comprising at least a transmission and a hybrid drive as its drive assembly.
From US 2005/0221947 A1 a method for operating a drive train of a motor vehicle that comprises an automatic transmission and a hybrid drive is known, in which a clutch is arranged between an internal combustion engine of the hybrid drive and an electric motor of the hybrid drive, and another clutch is arranged between the electric motor of the hybrid drive and the automatic transmission. When the drive train is being powered exclusively by the electric motor of the hybrid drive, according to the prior art the internal combustion engine of the hybrid drive can be started, such that while an upshift is taking place in the automatic transmission of the drive train, the clutch between the internal combustion engine of the hybrid drive and its electric motor is engaged. According to US 2005/0221947 A1 the electric motor of the hybrid drive is used in such a situation to start the internal combustion engine while a gearshift is being carried out, and accordingly during an interruption of traction force.